P.s. is the Semtech SX1276 also Class C compatible? I need no / very low latency for my project and can't seem to find this info on the site of Semtech. Do you also know if it's possible to implement this unit (and this driver) to the Pyboard v1.1?

Then I connected the second one to a ESP8266 board https://de.aliexpress.com/item/1PCS-Wir ... st=ae803_4 and got at startup:
Traceback (most recent call last):
File "main.py", line 11, in <module>
File "test.py", line 41, in main
File "controller.py", line 64, in add_transceiver
File "sx127x.py", line 97, in init
Exception: Invalid version.

Print out the version it shows version is 0.

I exchanged this board to ESP32 and there is no error message. This tells me, the problem is not at the SX1278.
I double checked more than once my wiring and cannot find any fault.
Test runs with MicroPython v1.9.4-8-ga9a3caad0 on 2018-05-11 and with esp8266-20190125-v1.10. Both same result.
By the way on ESP32 I use also esp8266-20190125-v1.10.

Perhaps someone should do the maths How much spare current capacity does the ESP8266 voltage regulator have? How much power does the LoRa device require? Should the LoRa device be powered from a separate 3.3V regulator?

Neither the ESP8266 chip itself, not the ESP8266 modules, have a 3.3V voltage regulator. There is usually a voltage regulator on the development boards, but it varies between the board make and version, so there is no single answer to that.